Method of polishing semiconductor copper interconnect integrated with extremely low dielectric constant material

ABSTRACT

A method of polishing metal and barrier layer interconnect integrated with an extremely low dielectric constant material includes steps of (A) preparing a wafer composed of a copper layer and the extremely low dielectric constant material, (B) treating the copper layer chemically to produce a hard and brittle surface residual formed on the surface of the copper layer, (C) keeping polishing the surface residual by ultrasonic waves, (D) polishing a barrier layer of wafer by the ultrasonic waves, thereby polishing the wafer successfully.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to technology ofpolishing wafer, and more particularly, to a method of polishing copper& Tantalum Nitride (Ta/TaN) interconnect integrated with an extremelylow dielectric constant material, which works on the surface of wafer bymeans of ultrasonic waves.

[0003] 2. Description of the Related Art

[0004] A conventional chemical mechanical polish method (CMP) can workon wafer with greater force. As to the wafer integrated with lowdielectric constant material, which is low in intensity, durability,hardness, and stability, it needs extremely low down and shear force topolish the wafer; otherwise, lead frame or dielectric layer or interfaceof the film on wafer will be spoiled. If the aforementioned extremelylittle force is made by decreasing a down force by a precise controltechnique, it will be difficult to manufacture such a particularmachine, which performs the precise control technique, and will cost alot of money. In addition, a barrier layer positioned on the wafer ismade of the chemically inert Ta/TaN, such that polishing the wafer withextremely little force is hardly possible. Hence, the conventionalmethod of polishing wafer with great force will hardly meet the futurerequirement of polishing copper & Ta/TaN, which are integrated withextreme-low dielectric constant material.

[0005] Furthermore, though another conventional method of polishingwafer without forces by chemical or electrochemical treatment,relatively to the mechanical pressure used by a conventional method ofpolishing wafer, applies no force on the surface of wafer, it merelysuccessfully works on a copper layer but ineffectively on the barrierlayer.

SUMMARY OF THE INVENTION

[0006] The primary objective of the present invention is to provide amethod of polishing metal and barrier layer interconnect integrated withan extremely low dielectric constant material, which improves thedrawbacks of the mechanical great force and the electrochemicalnon-force of the conventional polishing methods and is adapted to workon semiconductor copper interconnect integrated with the extremely lowdielectric constant material.

[0007] The foregoing objective of the present invention is attained bythe method of polishing metal and barrier layer interconnect integratedwith an extremely low dielectric constant material, which includes stepsof (A) preparing a wafer composed of a copper layer and the extremelylow dielectric constant material, (B) treating the copper layerchemically to produce a hard and brittle surface residual formed on thesurface of the copper layer, (C) keeping polishing the surface residualby ultrasonic waves, and (D) polishing a barrier layer of the wafer bythe ultrasonic waves, thereby polishing the wafer successful.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a schematic view of wafer on which the present inventionconstructed according to a first preferred embodiment is working;

[0009]FIGS. 2A, 2B, and 2C show the variations of the surface of thewafer during the polishing process constructed according to the firstpreferred embodiment of the present invention;

[0010]FIG. 3 is a schematic view of the wafer on which the presentinvention constructed according to a second preferred embodiment isworking;

[0011]FIG. 4 is a perspective view of the wafer on which the presentinvention constructed according to a second preferred embodiment isworking by means of ultrasonic waves; and

[0012]FIG. 5 is a schematic view of the wafer on which the presentinvention constructed according to a third preferred embodiment isworking.

DETAILED DESCRIPTION OF THE INVENTION

[0013] Referring to FIGS. 1 and 2, a method of polishing metal andbarrier layer interconnect integrated with an extremely low dielectricconstant material, which is constructed according to a first preferredembodiment of the present invention, includes steps as follows.

[0014] A. Prepare a wafer 10 composed of a copper layer 11 and theextremely low dielectric constant material 21; wherein, the copper layer11 is positioned over the low dielectric constant material 21, and abarrier layer 31 embodied as Tantalun Nitride which is a chemicallyinert, hard, and brittle ceramic material is positioned between thecopper layer 11 and the low dielectric constant material 21.

[0015] B. Treat the copper layer 11 chemically to produce a hard andbrittle surface residue layer 12 embodied as a cuprous compound layer onthe surface of the copper layer 11. For example, the cuprous compoundlayer can be cuprous oxide, which is preferably hard and brittle to beevenly polished by ultrasonic waves.

[0016] C. Apply the ultrasonic waves to a pad 51 to enable the pad 51 tomove and to further enable abrasive of abrasive slurry to polish thesurface residue layer 12, as shown in FIG. 2A, thereby removing thesurface residue layer 12 uniformly, as shown in FIG. 2B.

[0017] D. Apply the ultrasonic waves to the tool with the pad 51 toenable the pad 51 to move and to further enable the abrasive of theabrasive slurry to polish the barrier layer 31, thereby causing thepolished barrier layer 31 successfully, as shown in FIG. 2C.

[0018] In the present embodiment, the ultrasonic waves 90 applied to thepad 51 which contacts the surface of the wafer 10 can be transversal orlongitudinal waves; the transversal waves enable transversal travelingwaves or standing waves parallel to the surface of the wafer 10 to drivethe pad 51 to proceed elliptical movement, and meanwhile, a roughsurface of the pad 51 drives the abrasive of the abrasive slurry topolish the wafer 10; the longitudinal waves enable longitudinaltraveling waves or standing waves perpendicular to or crossed with thesurface of the wafer 10 at any angle to drive the abrasive of theabrasive slurry to reciprocate and impact on the wafer 10, andmeanwhile, the surface residue layer 12 of the wafer 10 is of brittlefracturing during polishing process; In addition, the transversal wavescan enable longitudinal traveling waves or standing waves parallel tothe surface of the wafer 10 to drive the pad 51 to reciprocate, andmeanwhile, the rough surface of the pad 51 drives the abrasive of theabrasive slurry to polish the wafer 10.

[0019] Referring to FIGS. 3 and 4, the method of polishing semiconductorcopper interconnect integrated with the extremely low dielectricconstant material, which is constructed according to a second preferredembodiment of the present invention, is different from theaforementioned embodiment only in steps C and D as follows.

[0020] C. Apply extremely great cavitation damage of cavitationgenerated by means of scanning of the ultrasonic waves 90 clustered byarray-type structure to the very surface and very micro area of thesurface residue layer 12′ to cause the brittle fracturing of the surfaceresidue layer 12′, thereby polishing the wafer 10 successfully.

[0021] D. Apply the extremely great cavitation damage of the cavitationgenerated by means of scanning of the ultrasonic waves 90 clustered byarray-type structure to the very surface and very micro area of thebarrier layer 31′ to cause the brittle fracturing of the barrier layer12′, thereby polishing the wafer 10 successfully.

[0022] In this embodiment, except the pad, only the cavitation generatedby the ultrasonic waves is applied to polish the surface of the wafer.

[0023] Referring to FIG. 5, the method of polishing semiconductor copperinterconnect integrated with the extremely low dielectric constantmaterial, which is constructed according to a third preferred embodimentof the present invention, is different from the aforementionedembodiments only in steps C and D in which the ultrasonic waves 90 areapplied to a pad 51″ to enable the pad 51″ to drive the abrasive slurry52″ to flow on the surface of the wafer 10″, thereby generating andapplying shearing force to polish the surface of the wafer 10″. Duringthe aforementioned process, the pad 51″ never touches the surface of thewafer 10″. The ultrasonic waves generate the hydrodynamic pressure forreducing the threshold pressure of the polishing process by eliminatingthe hydroplaning effect. Such kind of the ultrasonic polishing processis also worked as assistance to enhance the chemical treatment to renderuniform effect.

[0024] In light of above three preferred embodiments of the presentinvention, the polishing process of the copper layer can be done notonly by polishing the brittle and hard surface compound of the copperlayer by the ultrasonic waves, but also polishing the surface residuelayer of the soft material on the conventional copper layer by extremelylittle force generated by various applications of the ultrasonic waves,which causes uniform polishing effect.

[0025] Please be noted that the brittle surface residue layer 12generated by the chemical treatment is not only limited to a cuprouscompound layer but can be anything brittle generated by other chemicaltreatment.

[0026] In conclusion, the present invention utilizes the ultrasonicwaves 90 to proceed to micro polishing not only on the surface of thewafer 10 to avoid great mechanical force, but also effectively on thecopper layer 11 and the barrier layer 31. In addition, the pulse forceis generated during polishing process, such that the damage owing to theextremely low dielectric material could be avoided. Accordingly, thepresent invention effectively improves the drawbacks of the conventionalCMP and the conventional chemical polish.

What is claimed is:
 1. A method of polishing metal and barrier layerinterconnect integrated with an extremely low dielectric constantmaterial, said method comprising the steps of: (a) preparing a wafercomposed of a copper layer and the extremely low dielectric constantmaterial, said copper layer being positioned over the low dielectricconstant material, a barrier layer being positioned between said copperlayer and said low dielectric constant material; (b) treating saidcopper layer chemically to produce a hard and brittle surface residuelayer on the surface of said copper layer; (c) applying ultrasonicabrasion to said surface residue layer to cause the brittle fracturingof said surface residue layer, thereby rendering effective polishing ofsaid wafer; (d) applying the ultrasonic abrasion to said barrier layerto render effective polishing of said wafer.
 2. The method as defined inclaim 1, wherein said surface residue layer in the step (b) is a cuprouscompound.
 3. The method as defined in claim 2, wherein said cuprouscompound is cuprous oxide.
 4. The method as defined in claim 1, whereinsaid ultrasonic abrasion is worked by that apply ultrasonic waves to apad to enable said pad to move and to drive abrasive of abrasive slurryto abrade and polish said wafer.
 5. The method as defined in claim 4,wherein said ultrasonic waves applied to said pad are transversaltraveling or standing waves.
 6. The method as defined in claim 1,wherein said ultrasonic abrasion is worked by that apply cavitationgenerated by scanning of the ultrasonic waves clustered by array-typestructure to proceed to abrasion and polish.
 7. The method as defined inclaim 1, wherein said ultrasonic abrasion is worked by that apply theultrasonic waves to a pad to enable said pad to drive abrasive slurrywith abrasive to flow on the surface of said wafer, thereby generatingand applying shearing force to abrade and polish the surface of saidwafer.
 8. The method as defined in claim 7, wherein said ultrasonicwaves enable said abrasive slurry to generate hydrodynamic pressure viasaid pad for reducing the increasing relative velocity and the thresholdpressure of the polishing process, and work as assistance to enhance thechemical treatment to render uniform effect.